Electrochemical slurry compositions and methods for preparing the same

ABSTRACT

Embodiments described herein generally relate to semi-solid suspensions, and more particularly to systems and methods for preparing semi-solid suspensions for use as electrodes in electrochemical devices such as, for example batteries. In some embodiments, a method for preparing a semi-solid electrode includes combining a quantity of an active material with a quantity of an electrolyte to form an intermediate material. The intermediate material is then combined with a conductive additive to form an electrode material. The electrode material is mixed to form a suspension having a mixing index of at least about 0.80 and is then formed into a semi-solid electrode.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of U.S. ProvisionalApplication No. 61/659,248, filed Jun. 13, 2012, U.S. ProvisionalApplication No. 61/659,736, filed Jun. 14, 2012, U.S. ProvisionalApplication No. 61/662,173, filed Jun. 20, 2012, and 61/665,225, filedJun. 27, 2012, the disclosures of each of which are hereby incorporatedby reference in their entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under Grant NumberDE-AR0000102 awarded by the Department of Energy. The government hascertain rights in this invention.

BACKGROUND

Embodiments described herein generally relate to semi-solid suspensions,and more particularly to systems and methods for preparing semi-solidsuspensions for use as electrodes in electrochemical devices such as,for example, batteries.

Batteries are typically constructed of solid electrodes, separators,electrolyte, and ancillary components such as, for example, packaging,thermal management, cell balancing, consolidation of electrical currentcarriers into terminals, and/or other such components. The electrodestypically include active material, conductive material, binders andother additives.

Some known methods for preparing batteries include coating a metallicsubstrate (e.g., a current collector) with slurry composed of an activematerial, a conductive additive, and a binding agent dissolved in asolvent, evaporating the solvent, and calendering the dried solid matrixto a specific thickness. The electrodes are then cut, packaged withother components, infiltrated with electrolyte and the entire package isthen sealed.

Such known methods generally involve complicated and expensivemanufacturing steps such as casting the electrode and are only suitablefor electrodes of limited thickness, e.g., less than 100 μm. These knownmethods for producing electrodes of limited thickness result inbatteries with lower capacity, lower energy density, and a high ratio ofinactive components to active material. Furthermore, the binders used inknown electrode formulations can increase tortuosity and decrease theionic conductivity of the electrode. Thus, it is an enduring goal ofenergy storage systems development to simplify and reduce manufacturingcost, reduce inactive components in the electrodes and finished batteryand increase performance.

SUMMARY

Embodiments described herein generally relate to semi-solid suspensions,and more particularly to systems and methods for preparing semi-solidsuspensions for use as electrodes in electrochemical devices such as,for example, batteries. In some embodiments, a method for preparing asemi-solid electrode includes combining a quantity of an active materialwith a quantity of an electrolyte to form an intermediate material. Theintermediate material is then combined with a conductive additive toform an electrode material. The electrode material is mixed to form asuspension having a mixing index of at least about 0.80 and is thenformed into a semi-solid electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plot showing the effect of mixing methods on conductivity ofsemi-solid electrodes for a range of compositions, according to variousembodiments.

FIG. 2 is a plot showing the effect of mixing methods on yield stress ofsemi-solid electrodes for a range of compositions, according to variousembodiments.

FIGS. 3A-3C and FIGS. 4A-4C are schematic illustrations of semi-solidsuspensions, according to various embodiments.

FIG. 5 is a plot of the conductivity of a semi-solid electrode versusconductive additive loading, according to various embodiments.

FIGS. 6A-6C depict electrode slurry mixtures with different conductiveadditive loadings, according to various embodiments.

FIGS. 7-10 are plots illustrating rheological characteristics of slurryformulations, according to various embodiments.

FIGS. 11-13 are plots illustrating mixing curves, according to variousembodiments.

FIG. 14 is a plot illustrating the relationship of mixing index withspecific energy input and conductive additive loading, according tovarious embodiments.

FIG. 15 is a plot illustrating the effect of mixing on certain slurryparameters, according to various embodiments.

FIG. 16 is a plot illustrating the conductivity of certain slurries as afunction of mixing time.

FIGS. 17A-17D are micrographs of a slurry subjected to two differentmixing times, according to an embodiment.

FIG. 18 illustrates the evolution of mixing index and conductivity withmixing duration at 100 rpm, for two different cathode compositions.

FIG. 19 illustrates the evolution of mixing index and conductivity withmixing duration at 100 rpm, for two different anode compositions.

FIG. 20 is a plot illustrating conductivity as a function of mixing timefor two shear conditions, according to various embodiments.

FIG. 21 is a plot illustrating the loss of electrolyte with time, mixingduration and temperature, according to various embodiments.

FIG. 22 and FIG. 23 are plots illustrating the effect of temperature onviscosity, according to various embodiments.

FIG. 24 illustrates the mixing index over time for two differentexemplary cathode compositions.

FIG. 25 illustrates the mixing index over time for two differentexemplary anode compositions.

FIG. 26 illustrates the mixing index and conductivity for an anodecomposition prepared using various mixing processes.

FIG. 27 illustrates the mixing index and conductivity for two differentcathode compositions, prepared using two different mixing methods.

FIG. 28 illustrates the mixing index and conductivity for an anodecomposition mixed for two different mixing times.

FIG. 29 illustrates the effect of mixing time on stability duringprocessing for a first anode composition.

FIG. 30 illustrates the effect of mixing time on stability duringprocessing for a second anode composition.

FIG. 31 depicts two anode compositions and four different mixingdurations.

FIG. 32 illustrates the effect of mixing time on stability duringprocessing for a first cathode composition.

FIG. 33 illustrates the effect of mixing time on stability duringprocessing for a second cathode composition.

FIG. 34 depicts two cathode compositions and three different mixingdurations.

FIGS. 35A-35B illustrate the capacity of an exemplary semi-solid cathodeformulation as a function of charge and discharge rate, and a samplecharge/discharge curve.

FIGS. 36A-36B illustrate the capacity of an exemplary semi-solid cathodeformulation as a function of charge and discharge rate, and a samplecharge/discharge curve.

FIGS. 37A-37B illustrate the capacity of an exemplary semi-solid cathodeformulation as a function of charge and discharge rate, and a samplecharge/discharge curve.

FIGS. 38A-38B illustrate the capacity of an exemplary semi-solid cathodeformulation as a function of charge and discharge rate, and a samplecharge/discharge curve.

FIGS. 39A-39B illustrate the performance of a semi-solid basedelectrochemical cell over 100 cycles, and a sample charge/dischargecurve.

FIGS. 40A-40B illustrate the performance of a semi-solid basedelectrochemical cell over 30 cycles, and a sample charge/dischargecurve.

DETAILED DESCRIPTION

Embodiments described herein generally relate to semi-solid suspensions,and more particularly to systems and methods for preparing semi-solidsuspensions for use as electrodes in electrochemical devices such as,for example, batteries. In some embodiments, a method for preparing asemi-solid electrode includes combining a quantity of an active materialwith a quantity of an electrolyte to form an intermediate material. Theintermediate material is then combined with a conductive additive toform an electrode material. The electrode material is mixed to form asuspension having a mixing index of at least about 0.80 and is thenformed into a semi-solid electrode.

Consumer electronic batteries have gradually increased in energy densitywith the progress of the lithium-ion battery. The stored energy orcharge capacity of a manufactured battery is a function of: (1) theinherent charge capacity of the active material (mAh/g), (2) the volumeof the electrodes (cm³) (i.e., the product of the electrode thickness,electrode area, and number of layers (stacks)), and (3) the loading ofactive material in the electrode media (e.g., grams of active materialper cm³ of electrode media). Therefore, to enhance commercial appeal(e.g., increased energy density and decreased cost), it is generallydesirable to increase the areal charge capacity (mAh/cm²) of electrodes.One way to accomplish increasing the areal charge capacity, andtherefore reducing the relative percentage of inactive components, is byincreasing the thickness of the electrodes. Conventional electrodecompositions that use binders however, cannot be made thicker than about200 μm, because conventional electrode manufactured using the castingand high speed roll-to-roll calendering process tend to crack and/ordelaminate upon drying from the flat current collectors if they are madethicker than 200 μm. Additionally, thicker electrodes have higher cellimpedance, which reduces energy efficiency (e.g., as described in Yu etal “Effect of electrode parameters on LiFePO₄ cathodes”, J. Electrochem.Soc. Vol. 153, A835-A839 (2006)).

Embodiments of semi-solid electrode compositions and methods ofpreparation described herein can be manufactured directly with thesemi-solid suspension, thereby avoiding the use of conventional bindingagents and the electrode casting, drying, and calendering stepsaltogether. Some benefits of this approach include, for example: (i)simplified manufacturing with less equipment (i.e., less capitalintensive), (ii) the ability to manufacture electrodes of differentthicknesses (e.g., by simply changing a forming die dimension), (iii)processing of thicker (>200 μm) and higher capacity (mAh/cm²)electrodes, thereby decreasing the volume, mass, and cost contributionsof inactive components with respect to active material, and (iv) theelimination of binding agents (e.g., PVdF), thereby reducing tortuosityand increasing ionic conductivity of the electrode, as well asincreasing safety by excluding binders that can contribute to exothermicreactions. Examples of battery architectures utilizing semi-solidsuspensions are described in International Patent Publication No. WO2012/024499, entitled “Stationary, Fluid Redox Electrode,” InternationalPatent Publication No. WO 2012/088442, entitled “Semi-Solid FilledBattery and Method of Manufacture,” U.S. patent application Ser. No.13/607,021, entitled “Stationary Semi-Solid Battery Module and Method ofManufacture,” and U.S. patent application Ser. No. 13/606,986, entitled“Semi-Solid Electrode Cell Having a Porous Current Collector and Methodsof Manufacture,” the entire disclosure of each of which is herebyincorporated by reference.

As described herein, the term “about” generally means plus or minus 10%of the value stated, e.g. about 5 would include 4.5 to 5.5, about 10would include 9 to 11, about 100 would include 90 to 110.

Embodiments described herein relate generally to electrochemical devicessuch as, for example, lithium ion batteries, however, the systems,methods and principles described herein are applicable to all devicescontaining electrochemically active media. Said another way, anyelectrodes and/or devices including at least an active material (sourceor sink of charge carriers), an electronically conducting additive, andan ionically conducting media (electrolyte) such as, for example,batteries, capacitors, electric double-layer capacitors (e.g.,Ultracapacitors), pseudo-capacitors, etc., are within the scope of thisdisclosure.

In some embodiments, a method of preparing a semi-solid electrode (alsoreferred to herein as “semi-solid suspension” and/or “slurry” electrode)can include combining a quantity of an active material with a quantityof an electrolyte to form an intermediate material. The intermediatematerial is combined with an electrolyte and mixed to form an electrodematerial. The electrode material is mixed until a substantially stablesuspension forms that has a mixing index of at least about 0.8, at leastabout 0.9, at least about 0.95, or at least about 0.975, inclusive ofall ranges therebetween. In some embodiments, the electrode material ismixed until the electrode material has an electronic conductivity of atleast about 10⁻⁶ S/cm, at least about 10⁻⁵ S/cm, at least about 10⁻⁴S/cm, at least about 10⁻³ S/cm, or at least about 10⁻² S/cm, inclusiveof all ranges therebetween. In some embodiments, the electrode materialis mixed until the electrode material has an apparent viscosity of lessthan about 100,000 Pa-s, less than about 10,000 Pa-s, or less than about1,000 Pa-s, at an apparent shear rate of about 1,000 s⁻¹, inclusive ofall ranges therebetween. In some embodiments, the quantity of activematerial included in the electrode material can be about 20% to about75% by volume, about 40% to about 75% by volume, or about 60% to about75% by volume, inclusive of all ranges therebetween. In someembodiments, the quantity of electrolyte included in the electrodematerial can be about 25% to about 70% by volume, about 30% to about 50%by volume, or about 20% to about 40% by volume, inclusive of all rangestherebetween. In some embodiments, the quantity of conductive materialincluded in the electrode material can be about 0.5% to about 25% byvolume, or about 1% to about 6% by volume, inclusive of all rangestherebetween.

In some embodiments, the mixing of the electrode material can beperformed with, for example, any one of a high shear mixer, a planetarymixer, a centrifugal planetary mixture, a sigma mixture, a CAM mixtureand/or a roller mixture. In some embodiments, the mixing of theelectrode material can supply a specific mixing energy of at least about90 J/g, at least about 100 J/g, about 90 J/g to about 150 J/g, or about100 J/g to about 120 J/g, inclusive of all ranges therebetween.

In some embodiments, electroactive materials for the positive electrodein a lithium system include the general family of ordered rocksaltcompounds LiMO₂ including those having the α-NaFeO₂ (so-called “layeredcompounds”) or orthorhombic-LiMnO₂ structure type or their derivativesof different crystal symmetry, atomic ordering, or partial substitutionfor the metals or oxygen. M comprises at least one first-row transitionmetal but may include non-transition metals including but not limited toAl, Ca, Mg, or Zr. Examples of such compounds include LiCoO₂, LiCoO₂doped with Mg, LiNiO₂, Li(Ni, Co, Al)O₂ (known as “NCA”) and Li(Ni, Mn,Co)O₂ (known as “NMC”). Other families of exemplary electroactivematerials includes those of spinel structure, such as LiMn₂O₄ and itsderivatives, so-called “layered spinel nanocomposites” in which thestructure includes nanoscopic regions having ordered rocksalt and spinelordering, olivines LiMPO₄ and their derivatives, in which M comprisesone or more of Mn, Fe, Co, or Ni, partially fluorinated compounds suchas LiVPO₄F, other “polyanion” compounds as described below, and vanadiumoxides V_(x)O_(y) including V₂O₅ and V₆O₁₁.

In some embodiments, the active material comprises a transition metalpolyanion compound, for example as described in U.S. Pat. No. 7,338,734.In one or more embodiments the active material comprises an alkali metaltransition metal oxide or phosphate, and for example, the compound has acomposition A_(x)(M′_(1−a)M″_(a))y(XD₄)_(z),A_(x)(M′_(1−a)M″_(a))y(DXD₄)_(z), or A_(x)(M′_(1−a)M″_(a))y(X₂D₇)_(z),and have values such that x, plus y(1−a) times a formal valence orvalences of M′, plus ya times a formal valence or valence of M″, isequal to z times a formal valence of the XD₄, X₂D₇, or DXD₄ group; or acompound comprising a composition (A_(1−a)M″_(a))_(x)M′_(y)(XD₄)_(z),(A_(1−a)M″_(a))_(x)M′_(y)(DXD₄)_(z)(A_(1−a)M″_(a))_(x)M′_(y)(X₂D₇)_(z)and have values such that (1−a)_(x) plus the quantity ax times theformal valence or valences of M″ plus y times the formal valence orvalences of M′ is equal to z times the formal valence of the XD₄, X₂D₇or DXD₄ group. In the compound, A is at least one of an alkali metal andhydrogen, M′ is a first-row transition metal, X is at least one ofphosphorus, sulfur, arsenic, molybdenum, and tungsten, M″ any of a GroupIIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and VIBmetal, D is at least one of oxygen, nitrogen, carbon, or a halogen. Thepositive electroactive material can be an olivine structure compoundLiMPO₄, where M is one or more of V, Cr, Mn, Fe, Co, and Ni, in whichthe compound is optionally doped at the Li, M or O-sites. Deficienciesat the Li-site are compensated by the addition of a metal or metalloid,and deficiencies at the O-site are compensated by the addition of ahalogen. In some embodiments, the positive active material comprises athermally stable, transition-metal-doped lithium transition metalphosphate having the olivine structure and having the formula(Li_(1−x)l_(x))MPO₄, where M is one or more of V, Cr, Mn, Fe, Co, andNi, and Z is a non-alkali metal dopant such as one or more of Ti, Zr,Nb, Al, or Mg, and x ranges from 0.005 to 0.05.

In some embodiments, the lithium transition metal phosphate material hasan overall composition of L_(1−x−z)M_(1+z)PO4, where M comprises atleast one first row transition metal selected from the group consistingof Ti, V, Cr, Mn, Fe, Co and Ni, where x is from 0 to 1 and z can bepositive or negative. M includes Fe, z is between about 0.15 and −0.15.The material can exhibit a solid solution over a composition range ofO≦x≦0.15, or the material can exhibit a stable solid solution over acomposition range of x between 0 and at least about 0.05, or thematerial can exhibit a stable solid solution over a composition range ofx between 0 and at least about 0.07 at room temperature (22-25° C.). Thematerial may also exhibit a solid solution in the lithium-poor regime,e.g., where x≧0.8, or x≧0.9, or x≧0.95.

In some embodiments, the redox-active electrode material comprises ametal salt that stores an alkali ion by undergoing a displacement orconversion reaction. Examples of such compounds include metal oxidessuch as CoO, Co₃O₄, NiO, CuO, MnO, typically used as a negativeelectrode in a lithium battery, which upon reaction with Li undergo adisplacement or conversion reaction to form a mixture of Li₂O and themetal constituent in the form of a more reduced oxide or the metallicform. Other examples include metal fluorides such as CuF₂, FeF₂, FeF₃,BiF₃, CoF₂, and NiF₂, which undergo a displacement or conversionreaction to form LiF and the reduced metal constituent. Such fluoridesmay be used as the positive electrode in a lithium battery. In otherembodiments the redox-active electrode material comprises carbonmonofluoride or its derivatives. In some embodiments the materialundergoing displacement or conversion reaction is in the form ofparticulates having on average dimensions of 100 nanometers or less. Insome embodiments the material undergoing displacement or conversionreaction comprises a nanocomposite of the active material mixed with aninactive host.

In some embodiments, slurry components can be mixed in a batch processe.g., with a batch mixer that can include, e.g., a high shear mixture, aplanetary mixture, a centrifugal planetary mixture, a sigma mixture, aCAM mixture, and/or a roller mixture, with a specific spatial and/ortemporal ordering of component addition, as described in more detailherein. In some embodiments, slurry components can be mixed in acontinuous process (e.g. in an extruder), with a specific spatial and/ortemporal ordering of component addition.

In some embodiments, process conditions (temperature; shear rate or rateschedule; component addition sequencing, location, and rate; mixing orresidence time) can be selected and/or modified to control theelectrical, rheological, and/or compositional (e.g., uniformity)properties of the prepared slurry. In some embodiments, the mixingelement (e.g., roller blade edge) velocity can be between about 0.5 cm/sand about 50 cm/s. In some embodiments, the minimum gap between whichfluid is being flowed in the mixing event (e.g. distance from rollerblade edge to mixer containment wall) can be between about 0.05 mm andabout 5 mm. Therefore, the shear rate (velocity scale divided by lengthscale) is accordingly between about 1 and about 10,000 inverse seconds.In some embodiments the shear rate can be less than 1 inverse second,and in others it is greater than 10,000 inverse seconds.

In some embodiments, the process conditions can be selected to produce aprepared slurry having a mixing index of at least about 0.80, at leastabout 0.90, at least about 0.95, or at least about 0.975. In someembodiments, the process conditions can be selected to produce aprepared slurry having an electronic conductivity of at least about 10⁻⁶S/cm, at least about 10⁻⁵ S/cm, at least about 10⁻⁴ S/cm, at least about10⁻³ S/cm, or at least about 10⁻² S/cm. In some embodiments, the processconditions can be selected to produce a prepared slurry having anapparent viscosity at room temperature of less than about 100,000 Pa-s,less than about 10,000 Pa-s, or less than about 1,000 Pa-s, all at anapparent shear rate of 1,000 s⁻¹. In some embodiments, the processconditions can be selected to produce a prepared slurry having two ormore properties as described herein.

The mixing and forming of a semi-solid electrode generally includes: (i)raw material conveyance and/or feeding, (ii) mixing, (iii) mixed slurryconveyance, (iv) dispensing and/or extruding, and (v) forming. In someembodiments, multiple steps in the process can be performed at the sametime and/or with the same piece of equipment. For example, the mixingand conveyance of the slurry can be performed at the same time with anextruder. Each step in the process can include one or more possibleembodiments. For example, each step in the process can be performedmanually or by any of a variety of process equipment. Each step can alsoinclude one or more sub-processes and, optionally, an inspection step tomonitor process quality.

Raw material conveyance and/or feeding can include: batch based manualweighing of material with natural feeding (e.g., allowing the mixer toaccept material into the mixture without external force), batch basedmanual weighing of material with forced feeding either by a pistonmechanism or a screw-based “side stuffer,” gravimetric screw solidsfeeders with natural feeding (e.g., feed at the rate which the mixer cannaturally accept material), gravimetric screw solids feeders with forcedfeeding (e.g., units sold by Brabender Industries Inc combined with apiston mechanism or a screw-based ‘side stuffer’), and/or any othersuitable conveyance and/or feeding methods and/or any suitablecombination thereof.

In some embodiments, for example after mixing, the slurry can beconveyed and/or pressurized, for example using a piston pump,peristaltic pump, gear/lobe pump, progressing cavity pump, single screwextruder, conveying section of a twin screw extruder, and/or any othersuitable conveying device. In some embodiments, the torque and/or powerof the conveying device, the pressure at the conveying device exit, theflow rate, and/or the temperature can be measured, monitored and/orcontrolled during the conveying and/or pressurizing.

In some embodiments, for example after conveying and/or pressurizing,the slurry can be dispensed and/or extruded. The slurry can be dispensedand/or extruded using, for example, a “hanger die” sheet extrusion die,a “winter manifold” sheet extrusion die, a profile-style sheet extrusiondie, an arbitrary nozzle operable to apply a continuous stream ofmaterial to a substrate, injection into a mold of the correct size andshape (e.g., filling a pocket with material), and/or any other suitabledispensing device.

In some embodiments, after dispensing the slurry can be formed into afinal electrode. For example, the slurry can be calendar roll formed,stamped and/or pressed, subjected to vibrational settling, and/or cut indiscrete sections. Additionally, in some embodiments, unwanted portionsof material can be removed (e.g., masking and cleaning) and optionallyrecycled back into the slurry manufacturing process.

The systems, mixing equipment, processes and methods described hereincan be used to produce a semi-solid suspension (e.g., slurry) suitablefor use in electrochemical devices (e.g., batteries). The semi-solidsuspension produced by such systems and methods are suitable for theformulation of a slurry-based electrodes with particular properties, forexample, rheology, conductivity, and electrochemical performance. Forexample, some suitable mixing devices include batch mixers, such as,e.g., higher shear mixer, planetary mixer, centrifugal planetarymixture, sigma mixture, CAM mixture or roller mixture, C.W. Brabender orBanburry® style mixture, continuous compounding devices such as portedsingle or twin screw extruders (e.g., Leistritz, Haake), high shearmixers such as blade-style blenders, high speed kneading machines,and/or rotary impellers. In some embodiments, the mixing device can beoperable to control the flowability of the slurry regulating thetemperature, and/or to control the slurry homogeneity by modulating thechemical composition.

In embodiments in which a batch mixer is used to mix the semi-solidsuspension, the semi-solid suspension can be transferred from the batchmixer to another piece of processing equipment, e.g., an extruder. Insuch embodiments, the transfer method can be chosen so as to minimizeelectrolyte losses, to not appreciably disrupt the slurry state, and/orto not introduce other processing difficulties, such as entrainment ofambient gases. In embodiments in which an extruder (e.g., twin screw) isused to mix the semi-solid suspension, mixing and material conveyanceoccur together, thus eliminating a process step.

In some embodiments, some electrolyte loss can be tolerated and used asa control specification, and the amount that can be tolerated generallydecreases as electrolyte volume fraction increases and/or mixing indexincreases. For example, at a mixing index of 0.8, the maximumelectrolyte loss can be controlled to less than about 39%, to less thanabout 33%, or to less than about 27%. At a mixing index of 0.9, themaximum electrolyte loss can be controlled to less than about 5%, toless than about 4%, or to less than about 3%. At mixing indices higherthan 0.9, the maximum electrolyte loss can be controlled to less thanabout 5%, to less than about 4%, or to less than about 3%. Componentconcentrations can be calculated to determine and/or predict tolerablelosses, and vary according to the specific components. In otherembodiments, loss tolerances will be higher while in others they will bemore restrictive.

In some embodiments, the composition of the slurry and the mixingprocess can be selected to homogeneously disperse the components of theslurry, achieve a percolating conductive network throughout the slurryand sufficiently high bulk electrical conductivity, which correlates todesirable electrochemical performance as described in further detailherein, to obtain a rheological state conducive to processing, which mayinclude transfer, conveyance (e.g., extrusion), dispensing, segmentingor cutting, and post-dispense forming (e.g., press forming, rolling,calendering, etc.), or any combination thereof.

For example, FIG. 1 illustrates the electronic conductivity of differentslurry formulations and FIG. 2 illustrates the yield stress, arheological parameter, of the same slurry formulations, prepared using avariety of mixing methods including high sheared mixing, planetarymixing, planetary mixing with ultrasonication, handmixing, andhandmixing with ultrasonication. As illustrated in FIG. 1 and FIG. 2,there can be significant variation in the conductivity and yield stressof the slurry formulations when they are prepared using the differentmixing methods which demonstrates that mixing methods can have an effecton at least some of the characteristics and/or performance measures ofdifferent slurry formulations. In some embodiments, the mixing methodcan be selected to achieve one or more desired characteristic of thefinal prepared slurry. In some embodiments, maximizing a performancemeasure is not always the most desirable characteristic of the finalprepared slurry. Said another way, although producing a slurry having ahigh electronic conductivity is generally desirable, if the final slurryis not readily formable and/or stable, the high electronic conductivityfor that particular slurry would not be beneficial. Similarly, producinga slurry that is easily formable and/or very stable, but with a lowelectronic conductivity is also not desirable.

During mixing, the compositional homogeneity of the slurry willgenerally increase with mixing time, although the microstructure of theslurry may be changing as well. The compositional homogeneity of theslurry suspension can be evaluated quantitatively by an experimentalmethod based on measuring statistical variance in the concentrationdistributions of the components of the slurry suspension. For example,mixing index is a statistical measure, essentially a normalized varianceor standard deviation, describing the degree of homogeneity of acomposition. (See, e.g., Erol, M, & Kalyon, D. M., Assessment of theDegree of Mixedness of Filled Polymers, Intern. Polymer Processing XX(2005) 3, pps. 228-237). Complete segregation would have a mixing indexof zero and a perfectly homogeneous mix a mixing index of one.Alternatively, the homogeneity of the slurry can be described by itscompositional uniformity (+x %/−y %), defined herein as the range:(100%−y)*C to (100%+x)*C. All of the values x and y are thus defined bythe samples exhibiting maximum positive and negative deviations from themean value C, thus the compositions of all mixed material samples takenfall within this range.

The basic process of determining mixing index includes taking a numberof equally and appropriately sized material samples from the aggregatedmix and conducting compositional analysis on each of the samples. Thesampling and analysis can be repeated at different times in the mixingprocess. The sample size and volume is based on considerations of lengthscales over which homogeneity is important, for example, greater than amultiple of both the largest solid particle size and the ultimate mixedstate average intra-particle distance at the low end, and 1/Nth of thetotal volume where N is the number of samples at the high end.Optionally, the samples can be on the order of the electrode thickness,which is generally much smaller than the length and width of theelectrode. Capabilities of certain experimental equipment, such as athermo-gravimetric analyzer (TGA), will narrow the practical samplevolume range further. Sample “dimension” means the cube root of samplevolume. For, example, a common approach to validating the sampling(number of samples) is that the mean composition of the samplescorresponding to a given mixing duration matches the overall portions ofmaterial components introduced to the mixer to a specified tolerance.The mixing index at a given mixing time is defined, according to thepresent embodiments, to be equal to 1−σ/σ_(ref), where σ is the standarddeviation in the measured composition (which may be the measured amountof any one or more constituents of the slurry) and σ_(ref) is equal to[C(1−C)]^(1/2), where C is the mean composition of the N samples, so asthe variation in sample compositions is reduced, the mixing indexapproaches unity. It should be understood in the above description that“time” and “duration” are general terms speaking to the progression ofthe mixing event. Other indicators of mixing such as, for example,cumulative energy input to the mix, number of armature, roller, mixingblade, or screw rotations, distance traveled by a theoretical point oractual tracer particle in the mix, temperature of the mix (which isaffected by viscous heating), certain dimensionless numbers commonlyused in engineering analysis, and others can be used to predict orestimate how well the slurry is mixed.

In one embodiment, a total sample volume of 43 cubic centimeterscontaining 50% by volume active material powder with a particle sizedistribution with D50=10 um and D90=15 um, and 6% by volume conductiveadditive agglomerates powder with D50=8 um and D90=12 um in organicsolvent is prepared. This mixture can be used to build electrodes withan area of 80 cm², and a thickness of 500 μm. The sample dimensionshould be larger than the larger solid particle size, i.e., 15 μm, andalso the larger mixed state intra-particle length scale, i.e., about 16μm, by a predetermined factor. With a target of N=14 samples, the sampledimension should be less than 2,500 μm. The specific dimension ofinterest is in the middle of this range, i.e., 500 μm. Accordingly, toquantify mixing index, the samples are taken with a special tool havinga cylindrical sampling cavity with a diameter of 0.5 mm and a depth of0.61 mm. In this example, the sample volume would be 0.12 mm³.

In some embodiments, the sample volume selection for mixing indexmeasurement is guided by length scales over which uniformity isimportant. In some embodiments, this length scale is the thickness(e.g., 250 μm to 2,000 μm) of an electrode in which the slurry will beused. For example, if the electrode is 0.5 mm thick, the sample volumeshould preferably be on the order of (0.5 mm)³=0.125 mm³, i.e. betweenabout 0.04 mm³ and about 0.4 mm³. If the electrode is 0.2 mm thick, thesample volume should preferably be between 0.0025 and 0.025 mm³. If theelectrode is 2.0 mm thick, the sample volume should preferably bebetween 2.5 mm³ and 25 mm³. In some embodiments, the sample volume bywhich mixing index is evaluated is the cube of the electrodethickness±10%. In some embodiments, the sample volume by which mixingindex is evaluated is 0.12 mm³±10%. In one embodiment, the mixing indexis measured by taking N samples where N is at least 9, each samplehaving the sample volume, from a batch of the electrode slurry or from aformed slurry electrode that has a volume greater than the total volumeof the N samples. Each of the sample volumes is heated in a thermogravimetric analyzer (TGA) under flowing oxygen gas according to atime-temperature profile wherein there is 3 minute hold at roomtemperature, followed by heating at 20° C./min to 850° C., with thecumulative weight loss between 150° C. and 600° C. being used tocalculate the mixing index. Measured in this manner, the electrolytesolvents are evaporated and the measured weight loss is primarily thatdue to pyrolysis of carbon in the sample volume.

In some embodiments, a Brabender Batch Mixer can be used to mix theslurry at 30 to 100 rpm. In some embodiments, the slurry can be mixed at10-200 rpm or any other suitable speed. In some embodiments, the speedof the mixer can be varied throughout the mix cycle, for example, alower mix speed can be used to incorporate the ingredients, and a highermix speed can be used to homogenize the slurry. In some embodiments, themixing speed can be varied during the addition of the ingredients. Insome embodiments, the total mix time can be between 1 and 100 minutes.In other embodiments, any appropriate mix time can be selected. In someembodiments, the mixer can supply a specific mixing energy of between 3and 2,000 J/g. In other embodiments, the mixer can supply any suitableamount of mixing energy.

As described herein, conductive additives can have technicalcharacteristics and morphologies (i.e., hierarchical clustering offundamental particles) that influence their dispersive andelectrochemical behavior in dynamic and/or static suspensions.Characteristics that can influence dispersive and electrochemicalbehavior of conductive additives include surface area and bulkconductivity. For example, in the case of certain conductive carbonadditives, morphological factors can impact the dispersion of the carbonparticles. The primary carbon particles have dimensions on the order ofnanometers, the particles typically exist as members of largeraggregates, consisting of particles either electrically bound (e.g., byvan der Waals forces) or sintered together. Such agglomerates may havedimensions on the order of nanometers to microns. Additionally,depending on the surface energies of the particles, environment, and/ortemperature, aggregates can form larger scale clusters commonly referredto as agglomerates, which can have dimensions on the order of microns totens of microns.

When such conductive additives are included in a slurry, fluid shearingforces, e.g., imparted during mixing, can disrupt the carbon network,for example, by overcoming agglomerate and aggregate binding forces. Bydisrupting the conductive network, the additives can be present in afiner scale (more granular and more homogeneous) dispersion of theconductive solid. Mixing can also densify clusters of the conductivesolid. In some embodiments, mixing can both disrupt the conductivenetwork and densify clusters, which can sever electrical conductionpathways and adversely impact electrochemical performance.

FIG. 3A-3C are schematic diagrams of an electrochemically active slurrycontaining active material 310 and conductive additive 320 in which thequantity of the conductive additive 320 is not enough to form aconductive network. FIG. 3A depicts a slurry before any mixing energyhas been applied or after only minimal mixing energy has been applied.FIG. 3B depicts the slurry with an optimal amount of mixing energyapplied and FIG. 3C depicts the slurry with an excessive amount ofmixing energy applied. As illustrated in FIG. 3B even with the optimalamount of mixing, the amount of conductive additive 320 is not adequateto create an appreciable conductive network throughout the electrodevolume.

FIG. 4A-4C are schematic diagrams of an electrochemical active slurriescontaining an active material 410 and conductive additive 420. Contraryto FIG. 3A-C, in this example the quantity of the conductive additive420 is enough to form a conductive network. As shown in FIG. 4A, theconductive additive 420 is largely in the form of unbranchedagglomerates 430. The homogeneity of the conductive additive 420 couldbe characterized as non-uniform at this stage. As shown in FIG. 4B, theagglomerates 430 have been “broken up” by fluid shearing and/or mixingforces and have created the desired “wiring” of the conductive additiveagglomerate 440 interparticle network (also referred to herein as“conductive pathway”). As shown in FIG. 4C, the conductive network hasbeen disrupted by over mixing and the conductive additive 420 is now inthe from of broken and/or incomplete (or non-conductive) pathways 450.Thus, FIGS. 3A-3C and FIGS. 4A-4C illustrate that an electrochemicallyactive slurry can include a minimum threshold of conductive additive320/420 loading, and an optimal processing regime between two extremes(i.e., the slurry depicted in FIG. 4B). By selecting an appropriateloading of conductive additive 320/420 and processing regime, asemi-solid suspension can be formed having an appreciable conductiveinterparticle network (e.g., conductive additive agglomerate 440network). In some embodiments, the specific mixing energy applied can beabout 90 J/g to about 150 J/g, e.g., at least about 90 J/g, at leastabout 100 J/g, at least about 120 J/g or at least about 150 J/ginclusive off all ranges therebetween.

The quantity of a conductive additive, i.e., the mass or volume fractionof the conductive additive (also referred to herein as the conductiveadditive “loading”) that is used in a given mixture relative to othercomponents, such as an active material, that is suitable for the mixtureto achieve a specified level of bulk electrical conductivity depends onthe cluster state. Percolation theory can be used to select a loading ofconductive additive. Referring now to FIG. 5, a plot of conductivity ofan electrochemical slurry versus conductive additive loading is shown.As the loading of the conductive additive increases, so does theconductivity of the slurry. Three regions of conductivity are depictedon FIG. 5. At low loadings of conductive additive 522, the slurry hasrelatively low conductivity. For example, this slurry with lowconductive additive loading 522 can correspond to the slurry depicted inFIG. 3A-3C, in which there is insufficient conductive material to forman appreciable interparticle network. As the conductive additive loadingincreases, a percolating network 524 begins to form as chains ofconductive additive are able to at least intermittently provideconnectivity between active particles. As the loading increases further(e.g., as shown in the slurry depicted in FIGS. 4A-4C), a relativelystable interparticle networks 530 is formed. The shape and height of thepercolation curve can be modulated by the method of mixing an propertiesof the conductive additive, as described herein.

The amount of conductive additive used in a slurry, however, can beconstrained by other considerations. For example, maximizing batteryattributes such as energy density and specific energy is generallydesirable and the loading of active materials directly influences thoseattributes. Similarly stated, the quantity of other solids, such asactive material, must be considered in addition to the loading ofconductive material. The composition of the slurry and the mixingprocess described herein can be selected to obtain a slurry ofrelatively uniform composition, while enabling clustering of theconductive additive to improve electrical conductivity. In other words,the slurry can be formulated and mixed such that a minimum threshold ofconductive additive is included to form the interparticle network afteran appropriate amount of mixing, thereby maximizing the active materialloading. In some embodiments, the amount of conductive additive in theslurry can be about 0.5% to about 25% by volume, e.g., about 0.5%, 1%,6%, or 25% by volume, inclusive of all ranges therebetween. In someembodiments, the electronic conductivities of the prepared slurries canbe at least about 10⁻⁶ S/cm, at least about 10⁻⁵ S/cm, at least about10⁻⁴ S/cm, at least about 10⁻³ S/cm, or at least about 10⁻² S/cm,inclusive of all ranges therebetween.

In some embodiments, the maximum conductive additive loading at zeroactive material loading and the maximum active material loading at zeroconductive additive loading depend on the type of conductive additiveand active material being used. For example, a linear-type trend ofactive material to conductive additive, having a constant rheologicalparameter value (e.g., effective viscosity at a given shear rate) isgenerally observed, but other shapes (bowed out, bowed in, or with aninflection point) are possible. Said another way, a constant rheologicalparameter value can define a region in which “workable” formulations canbe selected. The region can depend on, for example, materials beingused, and can also be determined experimentally. In some embodiments, aworkable formulation can have up to about 20% by volume of a conductiveadditive with a surface area less than 40 m²/g, up to about 5% by volumeof a conductive additive with a surface area less than 1,000 m²/g, andup to about 52% by volume of lithium titanate with a tap density of 1.3g/cc.

In some embodiments, it is desirable for the electrochemically activeslurry to be “workable,” in order to facilitate material handlingassociated with battery manufacturing. For example, if a slurry is toofluid it can be compositionally unstable. In other words, thehomogeneity can be lost under exposure to certain forces, such asgravity (e.g., solids settling) or centrifugal forces. If the slurry isunstable, solid phase density differences, or other attributes, can giverise to separation and/or compositional gradients. Said another way, ifthe slurry is overly fluidic, which may be the result of low solidsloadings or a significantly disrupted conductive network, the solids maynot be sufficiently bound in place to inhibit particle migration.Alternatively, if an electrochemically active slurry is too solid, theslurry may break up, crumble, and/or otherwise segregate into pieces,which can complicate processing and dimensional control. Formulating theslurry within a band of adequate workability can facilitate easierslurry-based battery manufacturing. Workability of a slurry cantypically be quantified using rheological parameters which can bemeasured using rheometers. Some examples of different types ofrheometers that can be used to quantify slurry workability include:strain or stress-controlled rotational, capillary, slit, andextensional.

As described herein, the mixing speed (which may be fixed, staged,continuously varied, oscillated, and/or controlled according to afeedback signal) and duration of mixing (or of certain stages) canaffect the establishment and stability of electrical conductivity in thecarbon matrix and corresponding voltage efficiency in the cell, and thecompositional homogeneity amongst all material components. The formationand stability of electrical conductivity can be diminished by high shearor extended mixing. High shear and/or extended mixing, however, canfacilitate homogeneity, which can support local electrode balancing andlong cycle life. Additionally, material “workability,” which can enablemore efficient processing and handling during manufacture and/or longterm local compositional stability (e.g., no “settling” of solids withinthe finished electrode), can also be affected by mixing speed andduration.

Feeding of components to the mixer, extruder, or other combiningequipment can be facilitated by ram feeding chutes or similar fixeddisplacement devices. The rate at which components are fed into thecombining equipment can be set or controlled, which can limit shearhistory accumulation for material that is added first.

Active materials and conductive additives of different types, structure,morphology, and/or made by different processes can have differentinteractions with different components in the mixtures. This can resultin slurries having the same solid to electrolyte ratio with differentrheological properties.

In some embodiments, the ratios between active material, conductiveadditive, and electrolyte can affect the stability, workability, and/orrheological properties of the slurry. FIG. 6A-6C depict electrode slurrymixtures with different loadings of active material and conductiveadditive relative to the electrolyte. At a low loading 610 (FIG. 6A),i.e., a slurry in which there is relatively little active material andconductive additive relative to the electrolyte, can result in anunstable or “runny” mixture. As shown, phase separation, i.e.,separation of the of the active material and conductive additive (solidphase) from the electrolyte (liquid phase), can be observed in the lowloading 610 mixture. On the contrary, at a high loading mixture 630(FIG. 6C) where the maximum packing of solid materials in theelectrolyte has been exceeded, the mixture is too dry and is not fluidicenough to be conveyed or processed to a desired shape or thickness.Therefore, as shown in FIG. 6B, there is an optimal loading mixture 620where the slurry is stable (i.e., the solid particles are maintained insuspension) and is sufficiently fluidic to be workable into electrodes.

The “workable” slurries with different solids loadings can be evaluatedfor flowability and processability. The rheological behavior of theslurries can indicate processability under pressure driven flows, suchas in a single or twin screw extrusion and/or flow through a die. Theslurries can be categorized as “suspensions” with different loadinglevels and a low viscosity liquid medium/matrix. The flow behavior ofsuch suspensions can be dependent on size distribution, shape and volumefraction of solid particles, particle-particle and particle-matrixinteractions, and matrix rheology. In some embodiments, slurries can beselected based on rheology, which can be used to predict favorableprocessability of the slurries and/or desired electrochemicalperformance. The rheology of the “workable” slurries can be governed bythe compositional formulation, e.g., different active materials andconductive additives loaded at various concentrations and/or homogeneityof the slurries.

In some embodiments, a type and loading level of conductive additive canbe selected, which can form a gel like network that holds the suspensiontogether and can prevent separation. At this level of loading, differenttypes of conductive additives can, depending on their structure, formslurries with different rheological characteristics at the same loadinglevels. Alternatively, at a given volume loading level of activematerial, it is possible to pack different amounts and/or differenttypes of conductive additives into slurries that can have the samerheology. Similarly, the type of active material incorporated into theformulation at given volume loading level and type of conductiveadditive can effect the rheological properties of the slurries.Additionally, the particle size, aspect ratio and particle sizedistribution of the solids (e.g., the active material and/or theconductive additive) can impact the rheology of the slurry.

In some embodiments, the conductive additive can affect the rheology ofthe suspension. Thus, in such embodiments, at the same loading levels ofconductive additive, increasing concentrations of active materials cancontribute to the rheology of the slurry by increasing the shearviscosity of the suspension. FIG. 7 illustrates rheologicalcharacteristics including the apparent viscosity (η_(appr) Pa-s) andapparent shear rate (γ_(app) s⁻¹) for various formulations of slurriesthat are formulated from about 35% to about 50% by volume NMC and about6% to about 12% by volume of conductive additive C45. FIG. 8 illustratesthe rheological characteristics described herein for variousformulations of slurries formulated from about 35% to about 50% byvolume graphite (PGPT) and about 2% to about 10% by volume of theconductive additive C45. The apparent viscosity of the slurriesdescribed herein decreases as the apparent shear rate increases.

A capillary rheometer can be utilized to characterize rheologicalbehavior of slurries with different compositions. Capillary rheometersuse a pressure driven flow to determine, for example, processability ofa suspension by subjecting the material to shear rates higher than 10⁻¹s⁻¹. In a capillary rheometer, the suspension in a reservoir/barrel canflow through a capillary tube/die under pressure generated by a piston.The flow and deformation behavior of the suspension can be characterizedthrough generating flow rate versus pressure drop data by using variouscapillary dies with different diameters, lengths and entrance angels.

The flow of a suspension can be described by different mechanismsdepending on the suspension properties, i.e., yield stress, matrixviscosity, loading levels, particle interaction, and wall slip behaviorcontrolled by such properties. In some embodiments, the suspension canflow with or without slip. In some embodiments, the suspension can flowlike a plug without deformation at stresses below the yield stress. Thehighly loaded slurry suspension can be characterized by a strong slipmechanism and with a high yield stress of around 35,000 Pa.

The slurry suspensions can be prone to separation and flowinstabilities, structure development, mat formation and/or binderfiltration when flowing under a critical shear stress values due to alow viscosity liquid matrix in the formulation. Such behavior can becharacterized using a capillary rheometer using a small diameter and along L/D. The compositional formulation, especially conductive carbonloading levels, and the extrusion temperature can impact such structuralchanges during a pressure driven flow. FIG. 9 and FIG. 10 illustratetime-pressure graphs for various formulations of a first slurry thatincludes about 35%-50% NMC and about 6%-12% C45 (FIG. 9) and variousformulations of a second slurry that includes about 45%-50% PGPT andabout 2%-6% C45 (FIG. 10). As shown herein, varying amounts of pressureare required to dispense or flow a predefined quantity of slurry withina predetermined time period depending on the rheological characteristicsof the slurry, for example the apparent viscosity and the apparent shearrate. In some embodiments, the apparent viscosity of the prepared slurryat an apparent shear rate of about 1,000 s⁻¹ can be less than about100,000 Pa-s, less than about 10,000 Pa-s, or less than about 1,000Pa-s. In some embodiments, the reciprocal of mean slurry viscosity canbe greater than about 0.001 l/(Pa-s). Some slurry formulations includethree main components such as, for example, active material (e.g., NMC,lithium iron phosphate (LFP), Graphite, etc.), conductive additive(e.g., carbon black), and electrolyte (e.g., a mix of carbonate basedsolvents with dissolved lithium based salt) that are mixed to form theslurry. In some embodiments, the three main components are mixed in abatch mixer. In some embodiments, active materials are first added tothe mixing bowl followed by solvents. In some embodiments, theelectrolyte can be incorporated homogeneously with a dense activematerial without experiencing any ‘backing out’ of material from themixing section of the mixing bowl to form an intermediate material. Oncethe solvent and active materials are fully mixed, they can form a loose,wet paste. The conductive additive can be added to this intermediatematerial (i.e., loose paste), such that it can be evenly incorporatedinto the mix. In some embodiments, the active material can tend not toaggregate into clumps. In other embodiments, the components can becombined using another order of addition, for example, the solvent canbe added first to the mixing bowl, then the active material added, andfinally the additive can be added. In other embodiments, the slurry canbe mixed using any other order of addition.

The mixer (e.g., the batch mixer) can add dispersive shear energy to thebulk material being mixed. The mixing energy can be normalized to themass of material being mixed, which can provide a quantifiable metricfor how much work was done to mix a given sample. As mixing progresseswith time, mixing energy increases. At the beginning of a mixingoperation, when a relatively low amount of mixing energy has been addedto the slurry, the mixture can exhibit low homogeneity, e.g., materialmay not be evenly distributed throughout the bulk of the mixture.Additionally, a slurry having had a relatively small amount of mixingenergy added can have low flowability and/or formability. For example,if the liquid phase of the mixture has not been uniformly distributedamong the solid particles, aggregates of solid material (e.g., theconductive additive) can remain. In some embodiments, such aggregatescan be smaller than is visible to the naked eye, yet, these aggregatescan cause the slurry to be “dry” or “crumbly.” Furthermore, a slurryhaving a small amount of mixing energy can exhibit a lack of ductility,which can include the tendency of the material to fracture instead ofspread as it is formed.

As mixing energy increases, homogeneity of the mixture can increase. Ifmixing is allowed to continue, eventually excessive mixing energy can beimparted to the slurry. For example, as described herein, excessivemixing energy can produce a slurry characterized by low electronicconductivity. As mixing energy is added to the slurry, the aggregates ofconductive additive can be broken up and dispersed, which can tend toform a network like conductive matrix, as described above with referenceto FIGS. 3 and 4. As mixing continues, this network can degrade ascarbon particles are separated from each other, forming an even morehomogenous dispersion of carbon at the microscopic scale. Such anover-dispersion and loss of network can exhibit itself as a loss ofelectronic conductivity, which is not desirable for an electrochemicallyactive slurry. Furthermore, a slurry having excessive mixing energyimparted to it can display unstable rheology. As the carbon networkaffects mechanical, as well as electronic characteristics of the slurry,formulations which have been over mixed tend to appear “wetter” thanslurries subjected to a lesser amount of mixing energy. Slurries havingexperienced an excessive amount of mixing energy also tend to show poorlong term compositional homogeneity as the solids phases tend to settledue to gravitational forces. Thus, a particular composition can havefavorable electrical and/or rheological properties when subject to anappropriate amount of mixing. For any given formulation, there is arange of optimal mixing energies to give acceptable dispersion,conductivity and rheological stability.

FIGS. 11-13 are plots illustrating an example mixing curve, comparativemixing curves of low and high active material loading for the samecarbon additive loading, and comparative mixing curves of low and highcarbon additive loading for the same active material loading,respectively.

FIG. 11 depicts a mixing curve including the specific mixing energy1110, the speed 1140, and the torque 1170, of slurry, according to anembodiment. The first zone 1173 shows the addition of the raw materials.In some embodiments, the active material is added to the mixer, then theelectrolyte, and finally the conductive additive (carbon black). Thecarbon additive takes the longest time to add to the mixing bowl due tothe difficulty of incorporating a light and fluffy powder into arelatively dry mixture. The torque curve 1170 provides an indication ofthe viscosity, particularly, the change in viscosity. As the viscosityof the mixture increases with the addition of the carbon black, thetorque required to mix the slurry increases. The increasing viscosity isindicative of the mechanical carbon network being formed. As the mixingcontinues in the second zone 1177, the mixing curve shows the dispersionof the raw materials and relatively lower viscosity as evidenced by thedecreased torque required to mix the slurry.

FIG. 12 illustrates the difference between a low and high loading ofactive materials. It can be seen from this curve that the length of timeneeded to add the conductive carbon additive is approximately equal forlow and high active loadings, but the overall torque (and consequentlythe mixing energy) is much higher for the higher active loading. This isindicative of a much higher viscosity.

FIG. 13 illustrates the difference between a low and high conductivecarbon additive loading for the same active material loading. The mixingcurve for the high carbon loading includes the specific mixing energy1310, the speed 1340 and the torque 1373. The first zone 1373 shows theaddition of raw materials. As the viscosity of the mixture increaseswith the addition of the carbon black, the torque required to mix theslurry increases as seen in the first mixing zone 1375. The increasingviscosity is indicative of the carbon network being formed. As themixing continues in the second zone 1377, the mixing curve shows thedispersion of the raw materials and relatively lower viscosity asevidenced by the decreased torque required to mix the slurry. It shouldbe noted that the time needed to add the carbon conductive additive ismuch longer for the high carbon loading and the overall torque (andmixing energy) is also much higher. This mixing curve illustrates thatcarbon loading has a much higher impact on material viscosity thanactive material loading.

As described herein, compositional homogeneity of the slurry willgenerally increase with mixing time and the compositional homogeneitycan be characterized by the mixing index. FIG. 14 illustrates thespecific energy input required to achieve different mixing indexes forslurries of different conductive additive loadings. As shown, a higheramount of specific energy input is required to achieve the desiredspecific index, e.g., about 0.95 as the vol % of conductive additive isincreased in the slurry formulation. In some embodiments, the slurry ismixed until the slurry has a mixing index of about 0.8, of about 0.9, ofabout 0.95 or about 0.975, inclusive of all mixing indices therebetween.

FIG. 15 illustrates the effect of mixing on certain slurry parametersthat include the mixing index and the electronic conductivity of theslurry, according to an embodiment. The mixing index 1580 risesmonotonically while electronic conductivity 1590 initially increases (asconductive network is dispersed within the media), achieves a maximumvalue, and then decreases (network disruption due to “over mixing”).

In some embodiments, processing parameters can influence electronicconductivity, which is an important parameter for electrochemicallyactive slurries. For example, FIG. 16 demonstrates that processing timecan be selected to alter electronic conductivity and morphology of thesemi-solid electrodes. Examples of such results are shown in FIG. 16,which depicts the conductivity of certain slurries that include about35% NMC and about 2%-15% conductive additive C45, as a function ofmixing time. As seen in FIG. 16, longer mixing time can yield sampleswith lower conductivities.

Similarly, FIGS. 17A-17D are micrographs of a slurry subjected to twodifferent mixing times showing that carbon conductive additiveagglomeration tends to increase in a sample mixed for a longer time 1710(FIG. 17A-17B), as compared to a sample that was mixed for a shortertime 1720 (FIG. 17C-17D).

In some embodiments, the mixing time can have a simultaneously impactmixing index and conductivity of an electrode slurry. FIG. 18illustrates the effect of mixing time on the mixing index andconductivity of various slurry formulations that include about 45%-50%NMC and about 8% C45. Here, and in subsequently presented measurementsof mixing index, the mixing index is measured by taking sample volumesof 0.12 mm³ from a batch of the electrode slurry that has a total volumegreater than the sum of the individual sample volumes. Each samplevolume of slurry is heated in a thermo gravimetric analyzer (TGA) underflowing oxygen gas according to a time-temperature profile beginningwith a 3 minute hold at room temperature, followed by heating at 20°C./min to 850° C., with the cumulative weight loss between 150° C. and600° C. being used to calculate the mixing index. As shown in FIG. 18,the mixing index is observed to increase but the conductivity isobserved to decrease with increased mixing times. In these embodiments,a mixing time of about 2 minutes provided a good compromise between theconductivity and the mixing index, e.g., the slurry composition composedof 50% NMC and 8% C45 was observed to have a mixing index of about 0.95and a conductivity of about 0.02 S/cm. Any further mixing has a negativeimpact on the conductivity.

FIG. 19 illustrates the effect of mixing time on the mixing index andconductivity of various slurry formulations that include about 45%-50%PGPT and about 2%-4% C45. For the 50% PGPT and 2% C45 mixture, theconductivity is observed to initially rise, peaking at a 4 minute mixingtime, and then decrease by more than a factor of two at 24minutes—consistent with the trend described in FIG. 15. Therefore themixing times required to get an optimal mixing index and conductivity ofa slurry depend on the slurry formulation.

In some embodiments, shear rate can influence mixing dynamics andconductivity. As a result, in some embodiments, the selection of mixingelement rotation speed, container and/or roller size, clearancedimensions/geometry, and so forth can have an effect on conductivity.FIG. 20 is a plot depicting conductivity as a function of mixing timefor two different shear conditions. As shown, the slurry subjected tothe lower shear mixing 2010 is less sensitive to over mixing. The slurrysubject to higher shear mixing 2020 has a slightly higher peakconductivity, reaches the maximum conductivity with less mixing, and ismore sensitive to over mixing. In some embodiments, the optimal mixingtime can be 20 seconds, 2 minutes, 4 minutes or 8 minutes, inclusive ofmixing times therebetween.

In some embodiments, particle size, shape, aspect ratio, anddistribution of the solid particles in the slurry suspension can beselected to determine loading levels.

In some embodiments, temperature control during processing can beemployed, which can reduce electrolyte evaporation. By controlling thetemperature of the slurry, rheology, conductivity, and/or othercharacteristics of the slurry can be improved.

In some embodiments, the electrolyte can include a mixture of solventswith differing levels of volatility and vapor pressures. Temperature canhave an effect on the evaporation rate of this mixture as well as whichcomponents will preferentially evaporate before others, which can changethe composition and/or the performance of the electrolyte. FIG. 21depicts the percentage loss of electrolyte with temperature and mixingduration. Reduced total electrolyte and loss of the more volatilecomponents of the electrolyte in the slurry mixture can reduce the ionicconductivity of the slurry, subsequently increasing the voltagepolarization and decreasing the efficiency and capacity of the battery.By reducing and/or controlling processing temperatures, evaporation andsubsequent changes to the composition of the slurry can be decreased,and can lead to a more easily controllable process.

In some embodiments, for example, where electrolyte loss occurs, a“compensation” step can be added to the process. This step can includeadding a surplus of the electrolyte and/or components of the electrolyte(e.g., the more volatile electrolyte components) during some stage ofthe processing. The stage at which this addition is made could be duringinitial mixing of the electrolyte, during final cell assembly or at anyother step.

In some embodiments, temperature control can also be used to controlelectrolyte viscosity, which can affect the rheological behavior of theslurry. FIG. 22 illustrates the effect of varying temperature on theapparent viscosity and apparent shear stress of an anode slurrycomposition that includes about 45% PGPT and about 4% C45, according toan embodiment. The anode slurry was formulated at a first temperature of−2 degrees Celsius and a second temperature of 5 degrees Celsius. As thetemperature of the slurry and/or electrolyte decreases, the viscosityincreases. As the viscosity of the electrolyte increases, the force itexerts on the solid particles in suspension as it flows increases.Electrolyte and/or slurries with higher viscosities will tend todecrease the propensity of the solid components of the slurry (activeand conductive additive) to move slowly and build up into ‘plugs’ ofsolid material. FIG. 23 illustrates the effect of varying temperature onthe apparent viscosity and shear stress of a cathode slurry compositionthat includes about 50% NMC and about 8% C45, according to anembodiment. The cathode slurry was formulated at a first temperature of5 degrees Celsius and a second temperature of approximately roomtemperature (RT) (e.g., 25 degrees Celsius). Similar to anode slurryformulation of FIG. 22, viscosity of the cathode slurry increases withdecreasing temperature

In some embodiments, the temperature of the electrolyte and/or theslurry can have an effect on the adhesion of the slurry to othermaterials, such as process equipment. At low temperatures, the slurrycan have a lower level of adhesion to typical materials used inprocessing. Conversely, when the slurry is applied to a substrate (e.g.,a metallic foil or polymer film) to which adhesion is desired, raisingthe slurry/substrate interface temperature can act to promote adhesion.

In some embodiments, a processing temperature can be approximately 10degrees Celsius. In some embodiments, the processing temperature can belower than 10 degrees Celsius. The processing temperature can beselected to increase the slurry flow stability, for example, bymodulating the viscosity of the liquid phase (e.g. electrolyte). Saidanother way, for a given flow geometry, slurry composition, and drivingforce, the slurry may experience loss of compositional uniformity (i.e.,segregate) at one temperature, but may experience no loss ofcompositional uniformity at a different temperature. In someembodiments, the slurry flow stability can be modified (e.g., bytemperature selection) to improve the conveyance of material throughprocess equipment (e.g., extruder, extrusion die, etc.). In someembodiments, the slurry flow stability can be modified to decreaseslurry adhesion to process equipment (e.g., calendar roll, cuttingblades, etc.). In some embodiments, the slurry flow stability can bemodified to cause desired adhesion to laminating substrates (e.g.,metallic foils or polymer films). In some embodiments, the processingtemperature can be selected to minimize, or otherwise control, theamount of electrolyte evaporation. In some embodiments, the processingtemperature can be varied throughout the process to achieve the desiredcharacteristics at different steps.

In some embodiments, ultrasonication can be used to modulate theconductive network in slurries. For example, vibratory excitation(ultrasonication, vibration, acoustical) can be applied to mixingdevices, conveying/compounding devices, and/or the slurry itself (in acontainer or in situ).

In some embodiments, conductive additives can have aggregation andagglomeration characteristics (surface energies and interparticleforces) that can be modulated by other means, including: temperature,exposure to light or other tuned radiation, application of electrical ormagnetic fields, use of additives in the liquid phase of the slurry,specialized coatings on active materials, addition of chemical moietiesto the conductive additive, and/or operation in an electrochemicaloperational configuration before, during, and/or after one or moreprocess steps. For example, a salt can be added before, during and/orafter processing.

Battery electrolyte can include one or more solvents, e.g., variousorganic carbonates. In some embodiments a battery electrolyte caninclude one more salts. In some embodiments, the electrolyte can containother additives, for example, surfactants, dispersants, thickeners,and/or any other suitable agents. In some embodiments, the additive canmodify the properties of the electrolyte, for example to facilitateflowability, processability, compositional stability, workability,and/or overall manufacturability. The additive can include, for example,fluorinated carbonate derivatives, such as those developed by Daikinindustries. These additives can modify slurry properties in desirableways, such as, for example: (1) increasing liquid phase viscosity—whichexpands the range of shear rates that can be used in processing whilemaintaining fluid-solid compositional homogeneity, (2) increasinglubricity—which expands the slipping region during flow and preserveshomogeneity, and possibly reduces energy inputs related to processing,(3) reducing mixture vapor pressures, leading to reduced losses duringprocessing in unconfined spaces, among others. In some embodiments,additives such as these may have adverse effects on electrochemicalperformance, however, the advantages they afford for battery productioncan outweigh adverse effects.

In some embodiments, the following battery architectures can utilize theapproaches described herein: (1) those in which both electrodes areslurry-based, (2) those in which one electrode is slurry-based and theother conventionally cast, (3) those where one electrode is slurry-basedand the other is designed to consume and utilize a gas-phase reactant,e.g. oxygen from air. Designs can include single anode-cathode pairs(unit cells), prismatic assemblies with a multiplicity of anode/cathodepairs stacked atop one another, spiral wound assemblies, jelly rollassemblies, and other variants.

In some embodiments, the active materials can include lithium titanate,graphite, silicon alloys, tin alloys, silicon-tin alloys, lithium ironphosphate, lithium transition metal oxides, magnesium compounds,bismuth, boron, gallium, indium, zinc, tin, antimony, aluminum, titaniumoxide, molybdenum, germanium, manganese, niobium, vanadium, tantalum,iron, copper, gold, platinum, chromium, nickel, cobalt, zirconium,yttrium, molybdenum oxide, germanium oxide, or any other suitable activematerial. In some embodiments, the conductive additives can includecarbon (high e.g. Ketjen black or low e.g. C45, specific surface area,graphite—natural or manmade, graphene, nanotubes or othernano-structures, vapor grown carbon fibers, pelletized carbons, hardcarbon, et al), metal powders (e.g. aluminum, copper, nickel), carbides,and mixtures thereof. In some embodiments, the electrolytes included inthe slurries can include ethylene carbonate, propylene carbonate,butylene carbonate, and their chlorinated or fluorinated derivatives,and a family of acyclic dialkyl carbonate esters, such as dimethylcarbonate, diethyl carbonate, ethylmethyl carbonate, dipropyl carbonate,methyl propyl carbonate, ethyl propyl carbonate, dibutyl carbonate,butylmethyl carbonate, butylethyl carbonate, butylpropyl carbonate,y-butyrolactone, dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether,sulfolane, methylsulfolane, acetonitrile, propiononitrile, ethylacetate, methyl propionate, ethyl propionate, dimethyl carbonate,tetraglyme, and the like.

In some embodiments, the progression of mixing index over time for afixed RPM (e.g., 100 RPM) mixing speed can depend on the composition ofthe materials being mixed. For example, FIG. 24 illustrates the mixingindex at 100 rpm over time for a first cathode composition that includesabout 45% NMC and about 8% C45, and a second cathode composition thatincludes about 50% NMC and about 8% C45. The mixing index of FIG. 25illustrates the mixing index at 100 rpm over time for a first anodecomposition that includes about 45% PGPT and about 4% C45 and a secondanode composition that includes about 50% PGPT and 2% C45. In each case,nine samples having volumes in the range of about 0.1-0.2 cubicmillimeters were used to quantify the mixing index. As shown in FIG. 24and FIG. 25 the cathode and anode slurries show an increase in themixing index with mixing time. As shown in FIG. 25, the mixing indexcan, for example, plateau after a certain mixing time, e.g., 8 minutes,after which any more mixing does not cause an increase in the mixingindex.

In some embodiments, different mixing processes can produce differentdegrees of mixing (i.e., mixing index) and electrical conductivity forthe same anode and/or cathode composition. For example, FIG. 26illustrates the mixing index and electrical conductivity for an anodecomposition that includes about 35% PGPT and about 2% C45, mixed at afixed mixing speed of 100 RPM for 4 minutes with four different mixingtechniques (e.g., hand-mixed, roller, sigma and CAM). As shown, sigmaachieves better uniformity (i.e., higher mixing index), but rollerachieves higher electrical conductivity. Furthermore, CAM achieves thehighest uniformity (e.g., mixing index of about 0.96) and electricalconductivity (e.g., 0.33 S/cm) under these mixing conditions. FIG. 27illustrates the mixing index and electrical conductivity for a firstcathode composition that includes about 35% NMC and 8% C45 and a secondelectrode composition that includes about 45% NMC and 8% C45, both mixedat a fixed mixing speed of 100 RPM for 4 minutes with two differentmixing techniques (e.g., CAM and roller). While the 35% NMC/8% C45slurry achieves a higher mixing index with the roller mixer, the 45%NMC/8% C45 slurry achieves a higher mixing index with the CAM roller.

In some embodiments, the type of mixing process used can also have aneffect on the conductivity of the slurry. For example, FIG. 28,illustrates the mixing index and conductivity of an anode compositionthat includes about 45% PGPT and about 4% C45, mixed using a firstmixing process (e.g., roller blade) or a second mixing process (e.g. CAMblade) for a time period of 1 minutes or 4 minutes. As shown herein, forrelatively short mixing times (e.g. 1 minute), some mixing types (e.g.,roller) actually achieve higher uniformity than other mixing types(e.g., CAM). However, over time (e.g. 4 minutes), the mixing index forthe two types of mixing types reverses with the CAM producing higheruniformity. Furthermore, a higher conductivity can be achieved aftermixing for longer time periods (e.g., 0.45 S/cm) in some cases.

In some embodiments, the mixing time can affect the flowability of aslurry which is an indicator of slurry stability. For example FIGS.29-30 illustrate data from rheometer testing to assess the compositionalstability of a first anode slurry formulation, which includes about 45%PGPT and 4% C45, and a second anode slurry formulation that includes 50%PGPT and about 2% C45, respectively. Each of the first and the secondanode slurry formulations was mixed for 1 minute, 2 minutes, 4 minutesor 8 minutes. Under a stable set of process conditions, the pressurerequired to drive the slurry typically remains relativity constant intime. The timescale of pressure deviating from flat is an indicator ofstability. In FIG. 30, the first anode slurry formulation with thehighest stability is one with an intermediate mixing time of 4 minutes,slurries mixed for less (1 and 2 minutes) and more (8 minutes) are lessstable. In FIG. 30, a similar trend is observed for the second anodeslurry formulation. FIG. 31 shows micrographs of the first anode slurryand the second anode slurry which were mixed for the various timeperiods as described herein. As shown herein, the first and the secondanode slurry mixed for 4 minutes are the most stable.

Referring now to FIGS. 32-33, data from rheometer testing to assess thecompositional stability of a first cathode slurry formulation thatincludes about 50% NMC and 8% C45, and a second cathode slurryformulation that includes 45% NMC and about 8% C45, respectively. Eachof the first and the second cathode slurry formulations was mixed for 4minutes or 8 minutes. Results from slurries mixed at 1 minute are notshown as they were too unstable to hold shape. As shown in FIG. 30 andFIG. 31, the first and second cathode slurries mixed for 4 minutes or 8minutes show equally good rheological characteristics. FIG. 34 showsmicrographs of the first cathode slurry and the second cathode slurry,which were mixed for the various time periods as described herein. Asshown, the first and second cathode slurries mixed for 1 minute areunstable and breaking apart, while the first and second cathode slurriesmixed for 4 or 8 minutes are stable.

Conductivity, homogeneity, and rheological parameters like viscosity areslurry characteristics that can be measured outside of anelectrochemical cell. These are used as indicators of potentialelectrochemical performance, life, and processability, and are important“figures of merit” for slurries. That said, others parameters such as,for example, ionic conductivity, dynamic electrical response e.g.impedance, modulus of elasticity, wettability, optical properties, andmagnetic properties can be used as indicators of electrochemicalperformance.

In some embodiments, determining if a slurry has useful electrochemicalproperties can include verifying performance of the slurry in anelectrochemical cell. Discharge capacity at C/10 or higher current ratethat is of at least 80% of the theoretical capacity of the electrodeover a cell voltage range from 50% to 150% of the discharge voltage atwhich the magnitude of the differential capacity dQ/dV reaches a maximumcan serve as a reference definition for a slurry to have usefulelectrochemical properties. The following examples show theelectrochemical properties of various semi-solid electrodes formed usingthe slurry preparation methods described herein. These examples are onlyfor illustrative purposes and are not intended to limit the scope of thepresent disclosure.

Example 1

An LFP semi-solid cathode was prepared by mixing 45 vol % LFP and 2 vol% carbon black with an ethylene carbonate/dimethyl carbonate/LiPF₆ basedelectrolyte. The cathode slurry was prepared using a batchmixer with aroller blade fitting. Mixing was performed at 100 rpm for 2 minutes. Thesemi-solid slurry had a mixing index greater than 0.9 and a conductivityof 1.5×10⁻⁴ S/cm. The slurry was made into an electrode of 250 μmthickness and was tested against a Li metal anode in a Swagelok cellconfiguration. The cell was tested using a Maccor battery tester and wascycled between a voltage range of V=2-4.2 V. The cell was charged usinga constant current-constant voltage with a constant current rate at C/10and C/8 for the first two cycles then at C/5 for the latter cycles. Theconstant current charge is followed by a constant voltage hold at 4.2 Vuntil the charging current decreased to less than C/20. The cell wasdischarged over a range of C-rates between C/10 and 5 C.

FIG. 35A illustrates the charge and discharge capacities as a functionof the discharge C-rate for the semi-solid electrode of Example 1, and35B illustrates a representative charge and discharge curve at lowC-rates. The nominal cell capacity of 2.23 mAh corresponds to completeutilization of the LFP cathode active material. It is seen that amajority of the cell capacity is obtained under the test conditions forC-rates up to 1 C.

Example 2

An NMC semi-solid cathode was prepared by mixing 45 vol % NMC and 8 vol% carbon black with an ethylene carbonate/dimethyl carbonate/LiPF₆ basedelectrolyte. The cathode slurry was prepared using a batchmixer with aroller mill blade fitting. Mixing was performed at 100 rpm for 4 minutesso that the semi-solid slurry had a mixing index greater than 0.9 and aconductivity of 8.5×10⁻³ S/cm. The cathode was tested against a Li metalanode using the same cell configuration as in Example 1. The cell wastested using a Maccor battery tester and was cycled between a voltagerange of V=2-4.3 V. The cell was charged using a constantcurrent-constant voltage with a constant current rate at C/10 and C/8for the first two cycles then at C/5 for the latter cycles. The constantcurrent charge was followed by a constant voltage hold at 4.2 V untilthe charging current was less than C/20. The cell was discharged over arange of C-rates between C/10 and 5 C.

FIG. 36A illustrates the charge and discharge capacities as a functionof the discharge C-rate for the semi-solid electrode of Example 2, and36B illustrates a representative charge and discharge curve at lowC-rates. The nominal cell capacity of 3.17 mAh corresponds to completeutilization of the NMC cathode active material over the voltage rangetested. It is seen that a majority of the cell capacity is obtainedunder the test conditions for C-rates up to C/2.

Example 3

An NMC semi-solid cathode was prepared by mixing 55 vol % NMC and 4 vol% carbon black with an ethylene carbonate/dimethyl carbonate based/LiPF6based electrolyte. The cathode slurry was prepared using a batchmixerwith a roller blade fitting. Mixing was performed at 100 rpm for 4minutes so that the semi-solid slurry had a mixing index greater than0.9 and a conductivity of 8.4×10⁻⁴ S/cm. The cathode slurry was testedagainst Li metal using the same cell configuration and test procedure asin Example 2.

FIG. 37A illustrates the charge and discharge capacities as a functionof the discharge C-rate for the semi-solid electrode of Example 3, and37B illustrates a representative charge and discharge curve at lowC-rates. The nominal cell capacity of 2.92 mAh corresponds to completeutilization of the NMC cathode active material over the voltage rangeused. It is seen that a majority of the cell capacity is obtained underthe test conditions for C-rates up to C/2.

Example 4

An NMC semi-solid cathode was prepared by mixing 60 vol % NMC and 2 vol% carbon black with an ethylene carbonate/dimethyl carbonate/LiPF6 basedelectrolyte. The cathode slurry was prepared using a batchmixer with aroller blade fitting. Mixing was performed at 100 rpm for 4 minutes. Thecathode slurry was tested against Li metal using the same cellconfiguration and test procedure as in Example 2.

FIG. 38A illustrates the charge and discharge capacities as a functionof the discharge C-rate for the semi-solid electrode of Example 4, and38B illustrates a representative charge and discharge curve at lowC-rates. The nominal cell capacity of 3.70 mAh corresponds to completeutilization of the NMC cathode active material over the voltage rangeused. It is seen that a majority of the cell capacity is obtained underthe test conditions for C-rates up to C/2.

In some embodiments, cell stability under cycle testing can also be usedto evaluate slurries and/or electrochemical cell performance. Stabilitymeans sufficiently high retention of electrochemical capacity from cycleto cycle such as, for example, 99% or higher. The following examplesdemonstrate cell stabilities under cycle testing of two slurryformulations prepared using the semi-solid electrode preparation methodsdescribed herein.

Example 5

An NMC semi-solid cathode was prepared by mixing 35 vol % NMC and 8 vol% carbon black with an ethylene carbonate/dimethyl carbonate/LiPF₆ basedelectrolyte. The cathode slurry was prepared using a batchmixer with aroller blade fitting. Mixing was performed at 100 rpm for 4 minutes.This yielded a semi-solid cathode suspension having a mixing index of0.987 and a conductivity of 5×10⁻³ S/cm. A graphite semi-solid anode wasprepared by mixing 35 vol % graphite and 2 vol % carbon black in thesame composition electrolyte as used for the cathode. The anode slurryformulation was mixed at 100 rpm for 20 seconds to yield a semi-solidanode suspension having a mixing index of 0.933 and a conductivity of0.19 S/cm. The cathode and anode semi-solid slurries were formed intoelectrodes, each with 500 μm thickness. The electrodes were used to forma NMC-Graphite based electrochemical cell having active areas for bothcathode and anode of approximately 20 cm². The cell was cycled between2.75-4.2 V at various C rates. Over this voltage range the expectedspecific capacity of the NMC cathode is 155 mAh/g. The cell was cycledusing a constant current-constant voltage charging (CC-CV) and aconstant current discharge protocol between 2.75-4.2 V. At certainstages of testing a pulse charge and discharge test was performed(indicated on the plot by “DCR”). During the DCR test cycle, thecapacity value for that cycle is then appeared to be close to zero onthe plot (e.g. cycle 14^(th), 34^(th) and 55^(th)). For the constantcurrent-constant voltage charge steps, the cell was subjected to aconstant current at the rate specified e.g CC/10 and as the voltagelimit was reached, the cell was charged at a constant voltage until thecurrent drop below C/20 before it was switched to discharge. Constantcurrent was used for all discharging steps. The discharge current wasthe same current as the charge current on that cycle. For example, aCC-CV/10 cycle defined on the chart means that the cell was chargedusing a constant current of C/10, followed by a constant voltage chargeuntil the current value dropped to C/20. The cell was then discharge atC/10 until the lower voltage limit was reached. The number of cycle ofthat type of charge/discharge protocol is indicated as “x number ofcycle”. For example, “CC-CV/5×3” means that during that stage oftesting, the cells were charged at a constant current of C/5 followed bya constant voltage hold at 4.2V and the step was repeated 3 times.

FIG. 39A shows results of charge/discharge cycle results for theelectrochemical cell of Example 5. The electrochemical cell shows acapacity corresponding to about 160 mAh per gram of NMC in the firstcharge/discharge cycle, and maintains a capacity of about 120 mAh/g ofNMC even after 100 charge/discharge cycles. FIG. 39B shows arepresentative charge and discharge curve for the electrochemical cell.The measured cell capacity of the electrochemical cell was 215 mAh.

Example 6

An NMC semi-solid cathode was prepared by mixing 45 vol % NMC and 8 vol% carbon black with an ethylene carbonate/dimethyl carbonate/LiPF6 basedelectrolyte. The cathode slurry was prepared using a batchmixer with aroller blade fitting. Mixing was performed at 100 rpm for 4 minutes.This yielded a semi-solid cathode suspension having a mixing index of0.973 and a conductivity of 0.0084 S/cm. A graphite semi-solid anode wasprepared by mixing 50 vol % graphite and 2 vol % carbon black in thesame electrolyte as the cathode. The anode slurry formulation was mixedat 100 rpm for 20 seconds to yield a semi-solid anode suspension havinga mixing index of 0.962 and a conductivity of 2 S/cm. The cathode andanode semi-solid slurries were formed into electrodes each with 500 μmthickness. The electrodes were used to form a NMC-Graphite basedelectrochemical cell having active areas for both cathode and anode ofapproximately 20 cm². The cell was cycled using a constantcurrent-constant voltage charging (CC-CV) and a constant currentdischarge between 2.75-4.2 V with a similar protocol to that shown inExample 5. Over this voltage range the expected specific capacity of theNMC cathode is 155 mAh/g.

FIG. 40A shows results of charge/discharge cycle results for theelectrochemical cell of Example 6. The electrochemical cell shows acapacity corresponding to about 170 mAh per gram of NMC in the firstcharge/discharge cycle and maintains a capacity of about 100 mAh/g ofNMC after 30 charge/discharge cycles. FIG. 40B shows a representativecharge and discharge curve for the electrochemical cell. The measuredcell capacity of the electrochemical cell was 305 mAh.

While various embodiments of the system, methods and devices have beendescribed above, it should be understood that they have been presentedby way of example only, and not limitation. Where methods and stepsdescribed above indicate certain events occurring in certain order,those of ordinary skill in the art having the benefit of this disclosurewould recognize that the ordering of certain steps may be modified andsuch modification are in accordance with the variations of theinvention. Additionally, certain of the steps may be performedconcurrently in a parallel process when possible, as well as performedsequentially as described above. The embodiments have been particularlyshown and described, but it will be understood that various changes inform and details may be made.

The invention claimed is:
 1. A method of preparing a semi-solidelectrode, the method comprising: combining a quantity of an activematerial with a quantity of an electrolyte and a conductive additive toform an electrode material; mixing the electrode material to form asuspension having a mixing index of at least about 0.80; controlling atemperature of the electrode material during mixing to controlevaporation of the electrolyte therefrom; forming the electrode materialinto a semi-solid electrode; forming a second electrode; and forming anelectrochemical cell by combining the semi-solid electrode and thesecond electrode.
 2. The method of claim 1, wherein the electrodematerial is a stable suspension when it is formed into the semi-solidelectrode.
 3. The method of claim 1, wherein the electrode material ismixed until the suspension has a mixing index of at least about 0.90. 4.The method of claim 3, wherein the electrode material is mixed until thesuspension has a mixing index of at least about 0.95.
 5. The method ofclaim 4, wherein the electrode material is mixed until the suspensionhas a mixing index of at least about 0.975.
 6. The method of claim 1,further comprising: mixing the electrode material until the electrodematerial has an electronic conductivity of at least about 10⁻⁶ S/cm. 7.The method of claim 6, wherein the electrode material is mixed until theelectrode material has an electronic conductivity of at least about 10⁻⁵S/cm.
 8. The method of claim 7, wherein the electrode material is mixeduntil the electrode material has an electronic conductivity of at leastabout 10⁻⁴ S/cm.
 9. The method of claim 8, wherein the electrodematerial is mixed until the electrode material has an electronicconductivity of at least about 10⁻³ S/cm.
 10. The method of claim 9,wherein the electrode material is mixed until the electrode material hasan electronic conductivity of at least about 10⁻² S/cm.
 11. The methodof claim 1, further comprising: mixing the electrode material until theelectrode material has an apparent viscosity of less than about 100,000Pa-s at an apparent shear rate of 1,000 s⁻¹.
 12. The method of claim 11,wherein the electrode material is mixed until the electrode has anapparent viscosity of less than about 10,000 Pa-s at an apparent shearrate of 1,000 s⁻¹.
 13. The method of claim 12, wherein the suspension ismixed until the suspension has an apparent viscosity of less than about1,000 Pa-s at an apparent shear rate of 1,000 s⁻¹.
 14. The method ofclaim 1, wherein the quantity of the active material is about 20% toabout 75% by volume of the electrode material.
 15. The method of claim14, wherein the quantity of the active material is about 40% to about75% by volume of the electrode material.
 16. The method of claim 15,wherein the quantity of the active material is about 60% to about 75% byvolume of the electrode material.
 17. The method of claim 1, wherein thequantity of the electrolyte is about 25% to about 70% by volume of theelectrode material.
 18. The method of claim 17, wherein the quantity ofthe electrolyte is about 30% to about 50% by volume of the electrodematerial.
 19. The method of claim 18, wherein the quantity of theelectrolyte is about 20% to about 40% by volume of the electrodematerial.
 20. The method of claim 1, wherein the quantity of theconductive material is about 0.5% to about 25% by volume of theelectrode material.
 21. The method of claim 20, wherein the quantity ofthe conductive material is about 1% to about 6% by volume of theelectrode material.
 22. The method of claim 1, wherein the mixing indexis evaluated with a sample volume that is a cube of a formed semi-solidelectrode thickness±10%.
 23. The method of claim 1, wherein the mixingindex is evaluated with a sample volume of 0.12 mm³±10%.
 24. The methodof claim 1, wherein the controlling includes decreasing the temperatureof the electrode material during mixing.
 25. The method of claim 24,wherein the controlling includes decreasing the temperature of theelectrode material to lower than 10 degrees Celsius during mixing.
 26. Amethod of preparing a semi-solid electrode, the method comprising:combining a quantity of an active material with a quantity of anelectrolyte and a conductive additive to form an electrode material;mixing the electrode material to form a stable suspension having amixing index of at least about 0.80 and an electronic conductivity of atleast about 10⁻⁶ S/cm; and controlling a temperature of the electrodematerial during mixing to control rate of evaporation of the electrolytetherefrom.
 27. The method of claim 26, wherein the quantity of theactive material is about 20% to about 75% by volume of the stablesuspension, the quantity of the conductive additive is about 0.5% toabout 25% by volume of the stable suspension, and the quantity of theelectrolyte is about 25% to about 70% by volume of the stablesuspension.
 28. The method of claim 27, wherein the mixing supplies aspecific mixing energy of about 90 J/g to about 150 J/g to the electrodematerial.
 29. The method of claim 26, wherein the mixing supplies aspecific mixing energy of at least about 90 J/g to the electrodematerial.
 30. The method of claim 29, wherein the mixing supplies aspecific mixing energy of at least about 100 J/g to the electrodematerial.
 31. The method of claim 30, wherein the mixing supplies aspecific mixing energy of about 100 J/g to about 120 J/g to theelectrode material.
 32. A method of preparing a semi-solid electrode,the method comprising: combining an active material, an electrolyte, anda conductive additive in a vessel of a mixer; mixing the activematerial, the electrolyte, and the conductive additive in the mixer toform an electrode material suspension having a mixing index of at leastabout 0.80; and forming the electrode material into a semi-solidelectrode, wherein the mixing imparts a specific mixing energy to theactive material, the electrolyte, and the conductive additive so as tocontrol evaporation of the electrolyte therefrom.
 33. The method ofclaim 32, wherein the vessel of the mixer is cooled to a temperature oflower than 10 degrees Celsius during mixing.
 34. The method of claim 32,wherein the mixer is a high shear mixer.
 35. The method of claim 32,wherein the mixer is a planetary mixer.
 36. The method of claim 32,wherein the mixer is a centrifugal planetary mixer.
 37. The method ofclaim 32, wherein the mixer is a sigma mixer.
 38. The method of claim32, wherein the mixer is a CAM mixer.
 39. The method of claim 32,wherein the mixer is a roller mixer.